1. Technical Field
The invention relates to a lens assembly equipped with a lens for forming an image using subject light on an imaging device and to an imaging apparatus having the lens assembly.
2. Description of the Related Art
Recently, cameras become mounted in vehicles. Cameras provided in vehicles are used as surveillance cameras or as driving-assistance cameras. Since display screens have been provided on driver's seats as navigation systems have become popular, the latter case is intended to display an image taken by the camera on the display screen.
In such on-board cameras, most of those are required to have waterproof performance since those are mainly used outside of vehicles. In order to achieve sufficient waterproof performance without an increase in camera size in accordance with the requirement, it has been attempted to provide, in the on-board cameras, small-sized lens assemblies excellent in waterproof performance.
FIG. 6 is a view illustrating a section of a related-art lens assembly taken along an optical axis of a taking lens.
FIG. 6 shows a lens assembly 100 including a taking lens 101_1 of a first group, a taking lens 101_2 of a second group, a taking lens 101_3 of a third group, and a taking lens 101_4 of a fourth group in order from an incident side on subject light A. Furthermore, FIG. 6 shows a lens frame 102 that houses these taking lenses 101_1, 101_2, 101_3, and 101_4, and an O-ring 103 disposed between the taking lens 101_1 and the lens frame 102. The O-ring 103 is a rubber member that exhibits waterproof performance after the taking lens 101_1 is housed in the lens frame 102. Furthermore, a material of the O-ring 103 is an ethylene propylene based rubber, a silicon rubber, or the like.
JP 2002-90603 A (corresponding to U.S. Pat. No. 6,507,700) has proposed a technique that caulks a protrusion of a leading end of a lens frame on the front surface side of a taking lens by thermal adhesion in a state where the O-ring disposed between the outer peripheral surface of the taking lens and the inner surface of the lens frame is pressed.
In a related-art lens assembly, an O-ring is pressed by a taking lens and a lens frame, thereby securing waterproof performance. Here, the O-ring uses a rubber member. Hence, the surface of the O-ring is smooth. Generally, in a wide-angle taking lens for use in an on-board camera or a surveillance camera, a glass lens is used as a most-object side lens in order to obtain weather resistance. In the case where an outer peripheral surface of a glass lens is polished in order to perform centering, the outer peripheral surface is generally rougher than an optical functional surface. Hence, the outer peripheral surface, on which the O-ring is disposed, of the taking lens is rough. If the O-ring is pressed by the rough outer peripheral surface as described above, it is hard to make the O-ring be in sufficiently close contact with the outer peripheral surface. Accordingly, it is hard to sufficiently secure waterproof performance between the taking lens and the O-ring.